The invention is based on a device and a method for processing a packing material by means of ultrasound. DE 197 537 40 C1 discloses a device for processing a material strip, having an ultrasound unit which has a sonotrode and a counterpart tool. The material strip is guided through a gap between the sonotrode and counterpart tool, wherein the sonotrode is clamped in a carriage and can be adjusted relative to the counterpart tool by means of an adjusting device. The force with which the sonotrode is loaded in the direction of the counterpart tool is measured by means of a force sensor. By means of the pressing force of the sonotrode thus determined, the sonotrode can be moved toward the counterpart tool or away from the counterpart tool by means of a control device. The optimum pressing force is determined in advance in tests and is stored as a setpoint value in the control and/or regulating device.